A continuous distribution of sound energy, referred to as an “acoustic field” may be used for a range of applications including haptic feedback in mid-air. Such an acoustic field may be produced from a transducer array having known relative positions and orientations In this acoustic field, one or more control points may be defined. Such control points may have a known spatial relationship relative to the transducer array.
These control points may be assigned an amplitude and then amplitude-modulated with a signal and as a result produce vibro-tactile feedback in mid-air. An alternative method to produce feedback is to create control points that are not modulated in amplitude and move them around spatially to create “spatio-temporal” modulation that can be felt.
These control points are effectively concentrations of ultrasonic energy and moving them around generates disturbances in the air. By spatially modulating these disturbances created by ultrasonic foci, simply moving them backwards and forwards, it is possible to generate low frequency sound through the principle of acoustic radiation force as the focus pushes on the air or other materials around it.
Furthermore, very sudden disturbances are created when such focus points are quickly created or destroyed without slowly increasing or decreasing the amplitude. This creates pops or clicks which are often an unwanted side effect. Moving the control point can be used to achieve similar effects to changing the amplitude, but without the sharp changes in pressure that cause pops and clicks. This means that moving the control point is much more preferable than changing its amplitude. Due to the speed of sound being generally faster than the control point motion, this enables any generated pressure imbalances to dissipate, so the control point may be moved quickly without creating powerful air disturbances.
When considering the intersections between human hands and virtual objects, each finger and the palm in many instances feel a very small part of the overall shape that go towards the appreciation of the whole. Thus, when the hand feels a small part of the shape intersection the whole shape intersection must be created in order to not create and destroy the necessary control points. If the control points were created and destroyed such that they provide only the small part of the intersection, this would create unwanted noise. A more economical method of describing a shape therefore would save power and time and would then enable more of the power expended by the device to be used in creating haptic feedback in places which are touched by a hand.
Due to cross-modal and other perceptual effects, the induction of touch sensations through mid-air haptics remains surprisingly effective at communicating the existence, geometry and surface properties of objects. Fundamentally, although much research concentrates on exploration through touch alone, the effective use of these system is primarily used and driven through systems that cross multiple sensory modalities to provide an experience. For this reason, there exist in practice simple but conceptually complicated effects that can only be achieved through the realization of these underlying principles.
Furthermore, with mid-air haptic devices, virtual objects may be theoretically recreated in mid-air for the user to touch. But due to the nature of mid-air feedback, some fundamental physical limitations exist. This is because there are some parts of the somatosensory system that cannot be directly manipulated by the device, for example thermoreceptors for temperature sensing. But finding an optimal method to map output from the device—which necessarily has strengths and weaknesses peculiar to mid-air haptics—onto simulated physical interactions with virtual objects has been difficult. It is therefore valuable to develop an approach that is readily accepted by a human as corresponding to a plausible interaction with the object. Similarly, it is useful to manipulate focus point spinning in the air to generate a sound wave each time it moves along a path.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.